http://www.smogon.com/bw/pokemon/
As there is currently no data for you'll have to use the Pokemon here for reference.
http://veekun.com/dex/gadgets/stat_calculator
For Gen V pokemon and lower, you don't need to use Smogon to search for their base stats and then their corresponding IVs but for Gen VI Pokemon, you will need to do some researching and comparing with the Pokemon from Gen V and lower.
All you need to do is search for the Pokemon in their database and enter their corresponding nature, characteristic and stats, or you can just enter the Pokemon name yourself and enter since the name goes odd when I search for some Pokemon, like Mewtwo. Then enter the level and stats for your Pokemon and the calculator will work out your IVs for you.
The higher the level of your Pokemon, the more accurate the data you will receive. Given time, you will be able to do this really fast and may be able to estimate it yourself.
http://bulbapedia.bulbagarden.net/wiki/Characteristic
The characteristic of your Pokemon is something to look out for as it hints towards which stat has the highest IV for your Pokemon.